1,2,3-Trichloropropane

1,2,3-Trichloropropane (TCP) was historically produced as a byproduct in the manufacture of epichlorohydrin and allyl chloride, both important industrial intermediates. It was used commercially as a paint and varnish remover, cleaning agent, and fumigant component during the mid-20th century. [1] However, it came to prominence as an environmental contaminant in the 1980s–1990s when it was discovered as a common groundwater contaminant in agricultural regions of California and Hawaii — areas where the soil fumigant product D-D (1,3-dichloropropylene mixture containing TCP as an impurity) had been applied for decades to control nematodes in pineapple and other crops. Drinking water wells in these regions were found to contain TCP at concentrations far above any health-based threshold. [2] The NTP's 2-year bioassays were startling: TCP produced tumors in multiple organs (liver, kidney, forestomach, skin, and more) in both rats and mice of both sexes at doses relatively low by NTP standards, placing it among the most potent carcinogens evaluated by that program. The EPA classified it as a probable human carcinogen, and the California EPA established a public health goal for drinking water of 0.0007 µg/L — one of the most stringent values for any compound in drinking water. [3] Hundreds of water systems in California subsequently faced compliance challenges as TCP testing revealed widespread low-level contamination from historic fumigant use.

Drinking water is the primary exposure pathway for communities affected by historic agricultural fumigant use, particularly in California (San Joaquin Valley) and Hawaii. Historical industrial workers using TCP as a solvent were exposed by inhalation and skin contact. The general population's main current pathway is contaminated drinking water from groundwater sources in affected agricultural regions.

TCP's multi-organ carcinogenicity in both sexes of two species makes it one of the more potent carcinogens in the NTP bioassay database. The proposed mechanism involves bioactivation by glutathione S-transferase to an epoxide followed by DNA adduct formation in target tissues. [2] The extremely low drinking water health goal (0.0007 µg/L in California) reflects the high potency. Symptoms of acute TCP toxicity include liver and kidney damage, CNS depression, and irritation of the respiratory and GI tracts.

Residents in agricultural communities in California (especially Tulare, Fresno, Kings, and Madera counties), Hawaii, and similar regions where D-D fumigant was used historically and who rely on groundwater wells or small community systems are at highest risk. Historic industrial workers who used TCP as a solvent had significant exposures.

1. If you live in an agricultural region of California or Hawaii, check whether your water system has been tested for TCP; California has mandated testing for public water systems. 2. If your private well serves an area with historic fumigant use, test for TCP specifically. 3. Reverse osmosis filtration effectively removes TCP from drinking water. 4. Activated carbon filtration is less reliable for TCP compared to RO. 5. Contact your local water authority or state health department for testing resources in affected regions.